Pleural effusions frequently complicate inflammatory or infectious diseases. Of patients with pneumonia, for instance, 40% develop an effusion, which can impair pulmonary function and increase morbidity. This study of the physiology of the normal and inflamed pleura will examine those factors responsible for the imbalance of filtration and clearance which cause the accumulation of liquid. A comparative approach between species with different visceral pleuras will sort out the relative contribution of the visceral and parietal pleuras to clearance of effusions. Additional studies will center on lymphatic function. Normal pleural physiology studies will include the determination of the 1) liquid volume, 2) protein filtration (by tracer kinetics), 3) rate of clearance of liquid and protein (by artificial hydrothoraces), and 4) lymphatic clearance and pathways (by particle clearance, gamma imaging). Inflamed pleural studies will include the determination of the 1) protein filtration rate (by tracer kinetics), 2) rate of liquid and protein clearance (of artificial hydrothoraces), 3) response of the visceral and parietal pleuras (vascular labeling, histology, radiolabeled microspheres), and the 4) contribution of mediators and cells in formation of the effusion (inhibitor and depletion studies). The candidate, a pulmonary fellow in Norman Staub's laboratory, is already well acquainted with most of the experiments she proposes. She has performed experiments involving tracer kinetics, clearance of artificial hydrothoraces, and measurement of volume by dilution. She has had a long interest in pulmonary research and has both the desire and the potential for a research career. The San Francisco General Hospital and the Cardiovascular Research Institute have excellent facilities and personnel and are well equipped to support this research.